Its a 1 way valve for the brake servo. People normally tap off it for a boost guage reading.

It looks like your boost guage is now Teed into the FPR & the other has been blocked off with a screw.
 
Thanks for the reply, I found the pic online, can't upload pics of my car for some reason :s if I give seat a call do I just say I'm after a one way valve? Sorry about all the questions
 
Thanks for the reply, I found the pic online, can't upload pics of my car for some reason :s if I give seat a call do I just say I'm after a one way valve? Sorry about all the questions

Ask for the 1 way valve that fits between the inlet manifold & the brake servo. They will know what you mean.
 
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